This invention relates to automatic exposure time control devices using a photodiode as a light measuring element and, more particularly, to an automatic exposure time control device for a single reflex camera, wherein a photodiode receives scene light projected through an objective lens, produces a light measuring output voltage proportional to the logarithmic value of the object brightness, and then the output voltage is stored, and then logarithmically converted during exposure to thereby control the exposure time.
It is known that a photodiode is a better light measuring element as compared with a photoconductive element. As a light measuring element, it is necessary that the scene light projected through an objective lens be measured, then an electric current proportional to the brightness thereof be converted into a voltage proportional to that electric current by means of a logarithmic compressing diode, and that voltage be stored in a capacitor. The logarithmic compressing diode has a temperature characteristic and thus temperature-compensation commensurate with the diode temperature characteristic is required.